Materials, fabrication equipment, and methods for stable, sensitive photodetectors and image sensors made therefrom

ABSTRACT

Optically sensitive devices include a device comprising a first contact and a second contact, each having a work function, and an optically sensitive material between the first contact and the second contact. The optically sensitive material comprises a p-type semiconductor, and the optically sensitive material has a work function. Circuitry applies a bias voltage between the first contact and the second contact. The optically sensitive material has an electron lifetime that is greater than the electron transit time from the first contact to the second contact when the bias is applied between the first contact and the second contact. The first contact provides injection of electrons and blocking the extraction of holes. The interface between the first contact and the optically sensitive material provides a surface recombination velocity less than 1 cm/s.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/336,783, filed Jul. 21, 2014, which is a continuation of U.S. patentapplication Ser. No. 13/473,020, filed May 16, 2012, now issued as U.S.Pat. No. 8,785,908, which is a continuation patent application of U.S.patent application Ser. No. 12/506,233, filed Jul. 20, 2009, now issuedas U.S. Pat. No. 8,203,195, which is a continuation-in-part patentapplication of U.S. patent application Ser. No. 12/106,256, filed Apr.18, 2008, now issued as U.S. Pat. No. 7,923,801, which claims thebenefit of priority under 35 U.S.C. §119(e) to U.S. Patent ApplicationNo. 61/082,473, filed Jul. 21, 2008. U.S. Pat. No. 8,203,195 also claimsthe benefit of priority under 35 U.S.C. §119(e) to U.S. PatentApplication No. 61/154,751, filed Feb. 23, 2009, all of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention generally relates to optical and electronicdevices, systems and methods that include optically sensitive material,such as nanocrystal or other optically sensitive material, and methodsof making and using the devices and systems.

BACKGROUND

Optoelectronic devices, such as image sensors and photovoltaic devices,can include optically sensitive material. Example image sensors includedevices that use silicon both for the sensing function and for theread-out electronics and multiplexing functions. In some image sensors,optically sensitive silicon photodiodes and electronics can be formed ona single silicon wafer. Other example image sensors can employ adistinct material, such as InGaAs (for short-wave IR sensing), oramorphous selenium (for x-ray sensing), for the sensing (photon toelectron conversion) function. Example photovoltaic devices includesolar cells that use crystalline silicon wafers for photon to electronconversion. Other example photovoltaic devices can use a separate layerof material such as amorphous silicon or polycrystalline silicon or adistinct material for photon to electron conversion. However, theseimage sensors and photovoltaic devices have been known to have a numberof limitations.

INCORPORATION BY REFERENCE

Each patent, patent application, and/or publication mentioned in thisspecification is herein incorporated by reference in its entirety to thesame extent as if each individual patent, patent application, and/orpublication was specifically and individually indicated to beincorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a materials stack, under an embodiment.

FIG. 2 shows a cross-section of the materials stack over a portion of apixel, under an embodiment.

FIG. 3 shows a cross-section of the materials stack over a pixel, underan embodiment.

DETAILED DESCRIPTION

An optically sensitive device is described below. The device comprises afirst contact and a second contact, each having a work function, and anoptically sensitive material between the first contact and the secondcontact. The optically sensitive material comprises a p-typesemiconductor, and the optically sensitive material has a work function.The device comprises circuitry that applies a bias voltage between thefirst contact and the second contact. The magnitude of the work functionof the optically sensitive material is at least 0.4 eV greater than themagnitude of the work function of the first contact, and also at least0.4 eV greater than the magnitude of the work function of the secondcontact. The optically sensitive material has an electron lifetime thatis greater than the electron transit time from the first contact to thesecond contact when the bias is applied between the first contact andthe second contact. The first contact provides injection of electronsand blocking the extraction of holes. The interface between the firstcontact and the optically sensitive material provides a surfacerecombination velocity less than 1 cm/s.

An optically sensitive device is described below. The device comprises afirst contact, an n-type semiconductor, an optically sensitive materialcomprising a p-type semiconductor, and a second contact. The opticallysensitive material and the second contact each have a work functionshallower than 4.5 ev. The device comprises circuitry that applies abias voltage between the first contact and the second contact. Theoptically sensitive material has an electron lifetime that is greaterthan the electron transit time from the first contact to the secondcontact when the bias is applied between the first contact and thesecond contact. The first contact provides injection of electrons andblocks the extraction of holes. The interface between the first contactand the optically sensitive material provides a surface recombinationvelocity less than 1 cm/s.

A photodetector is described below. The photodetector comprises a firstcontact and a second contact, each having a work function. Thephotodetector comprises an optically sensitive material between thefirst contact and the second contact, the optically sensitive materialcomprising a p-type semiconductor, and the optically sensitive materialhaving a work function. The photodetector comprises circuitry thatapplies a bias voltage between the first contact and the second contact.The magnitude of the work function of the optically sensitive materialis at least 0.4 eV greater than the magnitude of the work function ofthe first contact, and also at least 0.4 eV greater than the magnitudeof the work function of the second contact. The photodetector comprisescircuitry that applies a bias voltage between the first contact and thesecond contact. The optically sensitive material provides a responsivityof at least 0.8 A/W when the bias is applied between the first contactand the second contact.

In the following description, numerous specific details are introducedto provide a thorough understanding of, and enabling description for,embodiments of the systems and methods. One skilled in the relevant art,however, will recognize that these embodiments can be practiced withoutone or more of the specific details, or with other components, systems,etc. In other instances, well-known structures or operations are notshown, or are not described in detail, to avoid obscuring aspects of thedisclosed embodiments.

Image sensors incorporate arrays of photodetectors. These photodetectorssense light, converting it from an optical to an electronic signal.Following is a description of numerous features, any one or acombination of which can be found in the photodetectors of anembodiment; the embodiments herein are not, however, limited to onlythese features.

The photodetectors of an embodiment are readily integrable with othercircuitry related to the image sensing function, such as circuits whichstore charge, circuits which relay signal levels to the periphery of thearray, circuits which manipulate these signal levels in the analogdomain, circuits which convert analog into digital signals, and circuitswhich process image-related data in the digital domain.

The photodetectors of an embodiment provide a maximum of sensitivity tolight within the wavelength band, or bands, of interest, along with lowdark current. Sensitivity is often quantified using the measuresignal-to-noise ratio (SNR) at a given level of illumination. Signal ismaximized when the responsivity, quantum efficiency, or gain of thedevice is maximized. Noise is minimized when random fluctuations inelectronic signals are minimized, subject to the limits prescribed bynatural fluctuations in electrical currents and voltages at a giventemperature. Relatedly, noise and other uncontrolled ordifficult-to-predict variations in background signal are generallyminimized when the magnitude of dark current is minimized.

The photodetectors of an embodiment provide a response time that isrelatively fast when compared to conventional photodetectors formedusing conventional processing methods. Applications such as videoimaging and shutterless still-image acquisition typically requirephotodetectors whose signal levels change substantially completely inresponse to a transient within fewer than 100 milliseconds (10 framesper second), or fewer than 33 milliseconds (30 frames per second), oreven 1 millisecond ( 1/1000 second exposure of a still image).

The photodetectors of an embodiment provide for the detection of a widerange of light intensities in a manner that can conveniently beprocessed by conventional electronic circuitry. This feature is known asproviding high dynamic range. One method of providing high dynamic rangeis to compress the measured electronic response as a function of theincident optical stimulus. Such compression can be referred to as asublinear, i.e. a nonlinear with decreasing slope, dependence ofelectrical signal on incident intensity. High dynamic range can also befacilitated by employing a photodetector whose gain can be controlled,such as through the selection of a voltage bias known to produce aspecific gain.

The photodetectors of an embodiment can provide for the discriminationamong different spectral bands of electromagnetic radiation. Ofparticular interest are the x-ray, ultraviolet, visible (including blue,green, and red), near-infrared, and short-wavelength infrared bands.

A description follows of methods and processes for creating, integrating(e.g., with circuits), and exploiting in a variety of applicationstop-surface photodetectors or arrays of photodetectors.

The photodetectors, and arrays of photodetectors, described herein canreadily be integrated with other portions of image sensor circuits andsystems by methods such as spin-coating, spray-coating, drop-coating,sputtering, physical vapor deposition, chemical vapor deposition, andself-assembly, to name a few. Embodiments include exchanging ligandspassivating nanoparticle surfaces for shorter ligands that will providefor appropriate charge carrier mobilities once films are formed.Embodiments include solution-phase exchanges which enable therealization of smooth-morphology films necessary to the realization ofimage sensors having acceptable consistent dark currents andphotoresponses across an array.

The photodetectors described herein provide relatively maximumsensitivity. They maximize signal by providing photoconductive gain.Values for photoconductive gain range from 1-50, resulting inresponsivities in, for example, the visible wavelengths ranging from 0.4A/W to 20 A/W. In embodiments, the photodetectors described hereinminimize noise by fusing nanocrystal cores such as to ensuresubstantially non-noise-degrading electrical communication among theparticles making up the optically sensitive layer through which currentflows. In embodiments, the photodetectors described herein minimize darkcurrent by minimizing the net doping of the active layer, thus ensuringthat the dark carrier density, and thus the dark conductance, of theseoptically sensitive materials is minimized. In embodiments, thephotodetectors described herein minimize dark current by providing anelectrode-to-nanocrystalline-layer electrical connection that blocks forexample one type of carrier, including potentially the majority carrierat equilibrium. In embodiments, cross-linking molecules are employedthat utilize chemical functionalities that remove oxides, sulfates,and/or hydroxides responsible for p-type doping. Thus, in embodiments, amore intrinsic or even n-type optically sensitive layer can be provided,leading to lowered dark currents. In embodiments, many steps in quantumdot synthesis and/or processing and/or device packaging can be performedin a controlled environment such as a Schlenk line or Glove Box; andoptically sensitive layers can be encapsulated using substantiallyimpermeable layers such as oxides, oxynitrides, or polymers such aspolyxylylene, or epoxies, in order to prevent reactive gases such asoxygen or water from significantly permeating the optically sensitivelayer. In this manner, combinations of properties such as gain, darkcurrent, and lag can be preserved over the useful lifetime of an imagesensor.

The photodetectors described herein provide a time-domain response thatcan be as rapid as approximately sub-100-milliseconds,sub-30-milliseconds, and sub-1-millisecond. In embodiments, this isachieved by providing gain-providing (and persistence-providing) trapstates associated with the optically sensitive layer that trap at leastone type of carrier for only a limited time period such as 100milliseconds, 30 milliseconds, or sub-1 millisecond. In embodiments, PbSnanoparticles are decorated with PbSO3, an oxide of PbS, which is shownto have a trap state lifetime in the vicinity of approximately 20-30milliseconds, providing for a transient response suited to many videoimaging applications. In embodiments, photodiodes are instead providedbased on colloidal quantum dot layers, wherein two electrical contactshaving appreciably different work functions are employed to contact theactive layer. In embodiments, dark currents can be minimized throughoperation of such devices without the application of an appreciableexternal voltage bias. In embodiments, cross-linking moieties such asbenzenedithiol, a bidentate linker, can be employed to remove and/orpassivate certain trap states that can be present, or can develop, insuch materials.

The photodetectors described herein provide enhanced dynamic range byproducing a sublinear dependence of electrical signal (such asphotocurrent). Over a region of low to middling intensities, trap statesare available to become filled, and escape occurs following somemoderate persistence, or trap state, lifetime, such as 30 millisecondsfor example. At higher intensities, these trap states becomesubstantially filled, such that charge carriers experience shorterlifetimes, or persistence times, corresponding to lower differentialgains. As a result these devices exhibit substantially constant gainsover a range of low to middling intensities, followed by a gentleroll-off in gain at higher intensities. Put another way, at low tomiddling intensities, photocurrent depends approximately linearly onintensity, but at higher intensities, photo current exhibits sub lineardependence on intensity. In embodiments, photodetectors are providedwherein photoconductive gain depends on the bias applied to a device.This arises because gain is proportional to carrier lifetime divided bycarrier transit time, and transit time varies in inverse proportionalitywith applied field. In embodiments, circuits are developed that exploitthis dependence of gain on bias to increase dynamic range.

In embodiments, photodetectors described herein are readily altered, or‘tuned’, to provide sensitivity to different spectral bands. Tuning isprovided herein through the quantum size effect, whereby nanoparticlediameter is decreased, in cases through synthetic control, to increasethe effective bandgap of the resulting quantum dots. Another method oftuning is provided through the choice of materials composition, whereinthe use of a material having a larger bulk bandgap generally facilitatesthe realization of a photodetector with responsivity onset at arelatively higher photon energy. In embodiments, photodetectors havingdifferent absorption onsets can be superimposed to form vertical pixels,wherein pixel(s) closer to the source of optical signal absorb and sensehigher-energy bands of electromagnetic radiation, whereas pixel(s)further from the source of optical signal absorb and sense lower-energybands.

FIG. 1 shows a materials stack, under an embodiment. The materials stackis integrated with complementary metal-oxide-semiconductor (CMOS)silicon circuitry, but is not so limited. The use of CMOS siliconcircuitry to read the signals transduced by photoconductivephotodetectors, including top-surface photodetectors, and includingthose based on colloidal quantum dots including PbS, includes theintegration of top-surface photoconductive materials with silicon CMOSelectronics. The structure and composition of the photoconductivephotodetector is described in detail below.

FIG. 2 shows a cross-section of the materials stack over a portion of apixel, under an embodiment. The figure depicts, in the left and righthand sides or regions, the same materials stack referenced in FIG. 1. Inthe lateral middle of the device is incorporated a discontinuity in thematerial metal ‘1’ which is replaced by material ‘7.’ Material ‘7’ canin general be an insulator such as SiO2 or SiOxNy. Embodiments of FIG. 2can be referred as a portion of a lateral pixel. In embodiments, currentsubstantially flows between metals ‘1’ through material ‘2’ (interface),material ‘3’ (adhesion), and material ‘4’ (photosensitive layer).Different portions or regions of the materials stack described hereinare referred to herein as “materials” or “layers” but are not solimited.

FIG. 3 shows a cross-section of the materials stack over a pixel, underan embodiment. Embodiments of FIG. 3 can be referred to as a portion ofa vertical pixel. The figure depicts with materials ‘1″2″3″4″5″6’generally the same materials stack as described above with reference toFIG. 1. An interface material or layer ‘8’ is incorporated or integratedon a top portion or region of the device. Material ‘8’ comprises amember or members of the sets of materials described herein as material‘2’. A metal or contact layer or material ‘9’ is incorporated orintegrated on a top portion or region of the device. The metal orcontact layer ‘9’ comprises a member or members of the sets of materialsdescribed herein as material ‘1’. In embodiments, material ‘9’ comprisesa transparent conductive material such as indium tin oxide, tin oxide,or a thin (substantially nonabsorbing to visible light) metal such asTiN, Al, TaN, or other metals recited below under material ‘1.’

Material “1” is a metal that lies above the substrate (not shown) andcan be a silicon CMOS integrated circuit. During processing it can be a200 mm or 300 mm wafer, i.e. a wafer that has not yet been singulated toform die. Material “1” refers to a metal, present at the top surface ofthe CMOS integrated circuit wafer, which is presented and available forphysical, chemical, and electrical connection with subsequent layers.The metal can include: TiN, TiO2, TixNy, Al, Au, Pt, Ni, Pd, ITO, Cu,Ru, TiSi, WSi2, and combinations thereof. Material “1” is referred to asthe contact, or the electrode, although it shall be discussed hereinthat the behaviour of this contact is influenced by thin layers that canreside between the metal and material “4”, the photoconductive quantumdot layer.

The metal can be chosen to achieve a particular work function, and caninfluence whether an ohmic or non-ohmic (e.g. Schottky) contact isformed with respect to the layers to which it is proximate. For example,the metal can be chosen to provide a shallow work function, such as avalue generally between −2.0 eV and −4.5 eV, for example values lyingbetween −2.0 eV and −4.2 eV.

The metal can achieve a surface roughness less than 5 nmroot-mean-squared.

The metal can be patterned with a critical dimension of 0.18 micrometersor smaller. The metal can be patterned such that, pixel-to-pixel, thespacing of the electrodes (such as between a pixel center electrode anda grid) does not vary by more than a standard deviation of 1%.

The metal can be terminated with an oxide such as a native oxide—such asTiOxNy in the case of TiN. In general this oxide, or other materialsatop it such as organic residues, inorganic residues such as ‘polymer,’etc. are of a consistent and known composition thickness.

The metal can be a conductive material, where the bulk of the materialconstituting the metal can have a resistivity that is less than 100microOhm*cm.

The metal can be processed such that, across the wafer, in all regionswhere light-sensing pixels are to be formed, it is not capped with anyadditional oxides or organics or contaminants.

The top surface of the wafer, prior to or after the formation of theinterface layer, can comprise regions of metal and insulating material(such as an insulating oxide), such that the peak-to-valley distance offeatures on this surface is less than 50 nm.

Prior to the introduction of the photosensitive semiconductor layer, theleakage current flowing between a pixel electrode in the center of a1.1×1.1 um or 1.4×1.4 um square grid electride should be less than 0.1fA at 3 V bias.

Layers or materials above material ‘1’ form an interface, or interfacelayer. Each of the layers forming the interface is described in detailbelow, in turn.

Material “2” is the first part or portion of the interface layer, andcomprises a material that resides atop the metal. Material ‘2’ cancomprise a pure, clean surface of the metal. The material of this layercan include oxides, including those generally formed, either throughexposure to water, oxygen, or other oxidizing species, as a result ofthe presence of the exposed metal; or it can be deliberately formed suchas through exposure to a controlled oxidizing environment and exposuresto elevated temperatures, such as in rapid thermal processing. Nativeoxides include, for example, the following: TiO2 and TiOxNy atop TiN;Al2O3 atop Al; Au2O3 atop Au; PtO or PtO2 on Pt; Ni2O3 atop Ni; WO3 atopW; PdO atop Pd; and oxygen-rich ITO atop ITO. It can be that such anative oxide is to be removed, such as using etching, and replaced withanother layer. For example, a native oxide such as TiOxNy can be etched(using a process such as argon sputtering) and then a layer can bedeposited on top of it such as a controlled oxide such as TiO2, TiOx, orTiOxNy. The sum of the thicknesses of native oxides anddeliberately-deposited oxides can be between 2 and 20 nm.

A portion of material ‘2’ can be a material that is substantiallytransparent to most or all wavelengths of visible light. It can have abandgap that is larger than 2 eV or larger than 2.5 eV or larger than 3eV. It can be a large-bandgap doped semiconductor. It can achieve dopingthrough stoichiometry, such as in the case of TiOx where x is variedbelow or above material 2 in order to achieve net doping. Values of xcan be typically 1.9 to achieve an excess of Ti over stoichiometricTiO2. Values of x can typically be 2.1 to achieve an excess of O overstoichiometric TiOx. TiOx where x<˜2 can be achieved by exposingstoichiometric TiO2 to a reducing environment. The density of freeelectrons can be increased, corresponding to greater n-type doping, byincrease the extent to which initially stoichiometric TiO2 is reduced,i.e. by decreasing x in TiOx more considerably relative to the value 2.TiO2 can be doped with nitrogen in order to modify its free carrierconcentration, work function, and electron affinity. TiO2 or TiOx can bedoped with B, C, Co, Fe. It can be a mildly n-type material such aslightly doped TiOx having an equilibrium carrier density of 10^10 cm-3.It can be a moderately doped n-type material such as TiOx having anequilibrium carrier density of 10^16 cm-3. It can be a more stronglydoped n-type material such as TiOx having an equilibrium carrier densityof 10^18 or 10^19 cm-3. Its electron affinity can correspondenergetically substantially closely with the work function of the metal.Its work function can correspond substantially closely with the workfunction of the metal. Its ionization potential can reside at an energythat is much deeper than the ionization potential of theoptically-absorbing layer (material ‘4’ described herein). It can beterminated through annealing processes, gas-phase treatments, orchemical treatments such as exposure to organic molecules, such as toachieve a low surface recombination velocity for holes when in contactwith an adjacent semiconductor layer such as the optically-absorbinglayer (‘4’ discussed below).

Material ‘3’ can also be present in the interface layer, and comprises amaterial that can be positioned or reside atop the first portion of theinterface layer. Material ‘3’ includes adsorbed organics such as organicmolecules, introduced deliberate or accidentally or through somecombination thereof, that reside above the metal, either in directcontact with the metal, or in direct contact with the metal oxide. Thesemolecules are discussed in detail herein.

Embodiments include material ‘2’ while material ‘3’ is absent. Suchembodiments include choices of materials in which no adhesion layer suchas that provided by material ‘3’ is required. As an example, if material‘2’ incorporates a metal such as titanium, such as if material ‘2’incorporates TiOx, and if material ‘4’ incorporates a crosslinker suchas mercaptobenzoic acid, in which one functional group on themercaptobenzoic acid binds the TiOx, then adhesion between material ‘4’and material ‘2’ can be provided without explicit inclusion of material‘3’.

In embodiments, all of material ‘1’ material ‘2’ and material ‘3’ can bepresent. Embodiments included cases where a Schottky contact is made viathe metal ‘1’ to the material ‘4’ without the deliberate introduction ofa heterojunction. Embodiments included a device in which TiN or TiOxNyforms the metal ‘1’, layer ‘2’ is a clean termination of the metal ‘1,’with no significant formation of a native oxide, an adhesion layer suchas hexamethyldisilazane is provided in material ‘3’.

In embodiments, all of material ‘1’ material ‘2’ and material ‘3’ can bepresent. Embodiments include cases where a heterojunction is formed viathe use of a large-bandgap oxide in material ‘2’ to the photosensitivelayer ‘4.’ Embodiments include a device in which TiN or TiOxNy forms themetal ‘1,’ layer ‘2’ includes a large-bandgap semiconductor such as TiOx(which can be structurally doped, impurity doped, both, or neither), andan adhesion layer such as hexamethyldisilazane can be provided inmaterial ‘3’.

In embodiments, material ‘1’ can be aluminum metal, material ‘2’ caninclude a native oxide of aluminum and can include a doped conductiveoxide such as doped Al2O3 and/or can include a large-bandgapsemiconductor such as TiOx (which can be structurally doped, impuritydoped, both, or neither), and material ‘3’ can include an adhesion layersuch as hexamethyldisilazane can be provided in material ‘3’.

In embodiments, material ‘1’ can include aluminum, gallium, indium, tin,lead, bismuth, magnesium, calcium, zinc, molybdenum, titanium, vanadium,lanthanum, chromium, manganese, iron, cobalt, nickel, copper, zirconium,niobium, palladium, silver, hafnium, tantalum, tungsten, iridium,platinum, gold. In embodiments, metals used in standard CMOS such asaluminum, tungsten, tantalum, titanium, copper can be preferred.

In embodiments, material ‘2’ can include a surface of the metal and caninclude oxides, nitrides, or oxynitrides of aluminum, gallium, indium,tin, lead, bismuth, magnesium, calcium, zinc, molybdenum, titanium,vanadium, lanthanum, chromium, manganese, iron, cobalt, nickel, copper,zirconium, niobium, palladium, silver, hafnium, tantalum, tungsten,iridium, platinum, gold. In embodiments, it can be preferred that itinclude oxides, nitrides, or oxynitrides of metals used in standard CMOSsuch as aluminum, tungsten, tantalum, titanium, copper.

In embodiments, material ‘2’ can comprise multiple sublayers. Inembodiments, it can comprise a sublayer consisting of a metal such asaluminum, gallium, indium, tin, lead, bismuth, magnesium, calcium, zinc,molybdenum, titanium, vanadium, lanthanum, chromium, manganese, iron,cobalt, nickel, copper, zirconium, niobium, palladium, silver, hafnium,tantalum, tungsten, iridium, platinum, gold. In embodiments, it can bepreferred that this sublayer can comprise metals used in standard CMOSsuch as aluminum, tungsten, tantalum, titanium, copper. In embodiments,material ‘2’ can comprise a further sublayer consisting of oxides,nitrides, or oxynitrides of aluminum, gallium, indium, tin, lead,bismuth, magnesium, calcium, zinc, molybdenum, titanium, vanadium,lanthanum, chromium, manganese, iron, cobalt, nickel, copper, zirconium,niobium, palladium, silver, hafnium, tantalum, tungsten, iridium,platinum, gold. In embodiments, it can be preferred that this furthersublayer include oxides, nitrides, or oxynitrides of metals used instandard CMOS such as aluminum, tungsten, tantalum, titanium, copper.

The layer referred to as material ‘4’ refers to an optically-absorbinglayer that includes nanocrystals, or quantum dots. A quantum dot (QD),depicted in ‘1220’ in FIG. 1, can be a nanostructure, for example asemiconductor nanostructure, that confines a conduction band electrons,valence band holes, or excitons (bound pairs of conduction bandelectrons and valence band holes) in all three spatial directions. Theconfinement can be due to electrostatic potentials (e.g., generated byexternal electrodes, doping, strain, impurities), the presence of aninterface between different semiconductor materials (e.g., in core-shellnanocrystal systems, incorporated in ‘1221’ of FIG. 1) or asemiconductor and another material (e.g., a semiconductor decorated byorganic ligands; or by a dielectric such as an oxide such as PbO, asulfite such as PbSO3, a sulfate such as PbSO4, or SiO2 incorporated in‘1221’ of FIG. 1), the presence of a semiconductor surface incorporatedin ‘1221’ of FIG. 1, or a combination of one or more of these. A quantumdot exhibits in its absorption spectrum the effects of the discretequantized energy spectrum of an idealized zero-dimensional system. Thewave functions that correspond to this discrete energy spectrum aresubstantially spatially localized within the quantum dot, but extendover many periods of the crystal lattice of the material. In one exampleembodiment, the QD can have a core of a semiconductor or compoundsemiconductor material, such as PbS. Ligands can be attached to some orall of the outer surface or can be removed in some embodiments. In someembodiments, the cores of adjacent QDs can be fused together to form acontinuous film of nanocrystal material with nanoscale features. Inother embodiments, cores can be connected to one another by linkermolecules. In some embodiments, trap states can be formed on the outersurface of the nanocrystal material. In some example embodiments, thecore can be PbS and trap states can be formed by an oxide such as PbSO3formed on the outer surface of core.

A QD layer can include a continuous network of fused QD cores, havingouter surfaces that are of a different composition than that in thecore, e.g., oxidized core material such as PbSO3, or a different kind ofsemiconductor. The individual QD cores in the film are in intimatecontact, but continue to exhibit many of the properties of individualquantum dots. For example, a lone (unfused) quantum dot has awell-characterized excitonic absorbance wavelength peak that arises fromquantum effects related to its size, e.g., 1-10 nm. The excitonicabsorbance wavelength peak of the fused QDs in the film is notsignificantly shifted from the central absorbance wavelength that waspresent prior to fusing. For example, the central absorbance wavelengthcan change by about 10% or less when fused. Thus, the QDs in the filmretain their quantum effects, despite the fact that they can be anintegral part of a macroscopic structure. In some embodiments, QD coresare linked by linker molecules as described further below. This allowscurrent to flow more readily than through unlinked, un fused QDs.However, the use of linker molecules to form a continuous film of QDsinstead of fusing the cores can reduce the dark current for some photoconductor and image sensor embodiments.

In some embodiments the QD layer is exceptionally radiation sensitive.This sensitivity is particularly useful for low-radiation imagingapplications. At the same time, the gain of the device can bedynamically adjusted so that the QDPC saturates, that is, additionalphotons continue to provide additional useful information that can bediscerned by the readout electronic circuit. Tuning of gain can beconveniently achieved by changing the voltage bias, and thus theresultant electric field, across a given device, e.g., a pixel. Someembodiments of QD devices include a QD layer and a custom-designed orpre-fabricated electronic read-out integrated circuit. The QD layer isthen formed directly onto the custom-designed or pre-fabricatedelectronic read-out integrated circuit. The QD layer can additionally bepatterned so that it forms individual islands. In some embodiments,wherever the QD layer overlies the circuit, it continuously overlaps andcontacts at least some of the features of the circuit. In someembodiments, if the QD layer overlies three-dimensional features of thecircuit, the QD layer can conform to these features. In other words,there exists a substantially contiguous interface between the QD layerand the underlying electronic read-out integrated circuit. One or moreelectrodes in the circuit contact the QD layer and are capable ofrelaying information about the QD layer, e.g., an electronic signalrelated to the amount of radiation on the QD layer, to a readoutcircuit. The QD layer can be provided in a continuous manner to coverthe entire underlying circuit, such as a readout circuit, or patterned.If the QD layer is provided in a continuous manner, the fill factor canapproach about 100%, with patterning, the fill factor is reduced, butcan still be much greater than a typical 35% for some example CMOSsensors that use silicon photodiodes. In many embodiments, the QDoptical devices are readily fabricated using techniques available in afacility normally used to make conventional CMOS devices. For example, alayer of QDs can be solution-coated onto a pre-fabricated electronicread-out circuit using, e.g., spin-coating, which is a standard CMOSprocess, and optionally further processed with other CMOS compatibletechniques to provide the final QD layer for use in the device. Becausethe QD layer need not require exotic or difficult techniques tofabricate, but can instead be made using standard CMOS processes, the QDoptical devices can be made in high volumes, and with no significantincrease in capital cost (other than materials) over current CMOSprocess steps.

The QD material can have an absorption cutoff approximately at the edgeof the visible, such as round 650 nm. The QD material can have anabsorption cutoff at longer wavelengths, in order to ensure a highabsorbance over the entire visible, such as when the absorption cutoffis in the 700-900 nm range.

The QD film can be deposited using conventional spin-on process, ink-jetprinting process, Langmuir-Blodgett film deposition, electrokineticsprays, or nano-imprint. The QD film can be deposited using dispensingof QD solution on a wafer at 30 RPM followed by three-step spin process.

The spectral position of the peak in the QD solution absorption can bespecified to lie at 740 nm, +/−10 nm. The ratio of the absorbance at theQD absorption peak near 740 nm, and the valley slightly to the blue ofthis peak, can be specified to be 1.2.

The thickness of the quantum dot layer can be specified to be 300nm+/−50 nm. The thickness of the quantum dot layer can be chosen toensure that, over the spectral range 400-640 nm, greater than 90% of alllight incident on the film is absorbed. The roughens (root-mean-squared)of the quantum dot film can be specified to be less than 5 nm.

The dark current in a 1.1×1.1 um pixel can be less than 0.5 fA undersuitable bias, such as a 3V bias. The gain can be greater than 10 in a1.1×1.1 um pixel.

Alklali metal impurities can be present at lower than 5E17 cm-3concentration in the quantum dot film. Defects greater than 0.16 micronsin size can be fewer than 20 across a 200 mm wafer. The mobility of theflowing carrier can exceed 1E-5 cm2/Vs. The loading fraction ofnanocrystals in the film can exceed 30% by volume.

Incorporated into material ‘4’ can be chemical species such as PbO,PbSO4, PbSO3, poly-sulfates; and they can also includephysically-adsorbed species such as O2, N2, Ar, H2, CO2, H2O, and H2S.

Incorporated into material ‘4’ can be molecules that are bound to thesurface of at least one nanoparticle, or nanocrystal, or quantum dot.These can include thiol-terminated ligands such as benzenethiol,ethanethiol; carboxylate-terminated molecules such as oleic acid andformic acid; amine-terminated ligands such as pyridine, butylamine,octylamine. They can also include bidentate cross linkers such asbenzenedithiol, ethanedithiol, and butanedithiol. They can also includemultidentate molecules that include (1) a backbone (2) certainsidegroups and/or endgroups that bind to the nanoparticle surface,including thiols, amines, carboxylates; and (3) other functional groupssuch as those that confer solubility in polar, nonpolar, and partiallypolar solvents.

Material ‘5’ can include layers on top of ‘4’ that can providepassivation of the underlying material, including minimizing the extentof movement of species between layers ‘1’-‘4’ of the materials stack andthe outside of the materials stack. This layer can also facilitate goodphysical adhesion with overlying layers such as encapsulant layers.

Material ‘6’ refers to a layer, or layers, that can be included on topof the material stack and can serve to minimize the extent of movementof species between layers ‘1’-‘4’ of the materials stack and the outsideof the materials stack. In a planar cell configuration the quantum dotfilm layer can be encapsulated against oxygen and moisture diffusionusing a low-temperature (less than 100° C.) PECVD SiO2, SiN, or SiOCNprocess providing optically transparent film suitable for furtherintegration with CFA. The film can be specified to have a thickness of200 nm+/−10 nm. It can be specified to have a surface roughness lessthan 5 nm rms. Optical transmittance can exceed 99%. Adhesion can beprovided to the underlying layers. An embodiment can have fewer thantwenty greater-than 0.1-um particle defects across a 200 mm wafer. Anembodiment can have fewer than twenty greater-than-0.1-um pinholesacross a 200 mm wafer.

The nature of the interface between the electrical contact and thelight-sensitive semiconductor is an important determinant of devicestability and performance. For example, whether the contact is ohmic vs.Schottky, and whether the contact and semiconductor are separated by athin interfacial layer which passivates at least one of the{semiconductor and the contact}, are important in stability andperformance.

The composition of the photoconductive layer—for example the presence ofsurface trap states on the semiconductor materials making up thephotoconductor—is an important determinant of device performance andstability. In particular, photoconductive materials are often sensitiveto the presence of physisorbed or chemisorbed species, possiblyoriginally presented as a gas (such as O2, H2O, CO2), on thenanoparticle surfaces—these must thus be carefully controlled duringprocessing, and an encapsulating and/or passivating layer(s) can beused, above and/or below, the photoconductive layer, to preserveconsistent photoconductive features over time. Further descriptionfollows of the interface between metal and semiconductor of anembodiment as well as encapsulation of an embodiment.

The layer ‘4’ can be made from silicon, including single-crystalsilicon, polycrystalline silicon, nanocrystalline silicon, or amorphoussilicon including hydrogenated amorphous silicon.

The layer ‘4’ can include materials that are not substantiallyquantum-confined, but instead substantially retain the bandgap of a bulksemiconductor. Embodiments include crystalline or polycrystalline ornanocrystalline or amorphous embodiments of materials such as silicon,gallium arsenide, carbon, PbS, PbSe, PbTe, Bi2S3, In2S3,Copper-Indium-Gallium-Selenide (or Sulfide), SnS, SnSe, SnTe, in whichthe characteristic size of any crystalline or partially-crystallinesubunits is typically not smaller than the Bohr exciton radius (thecharacteristic spatial extent of electron-hold pairs) in thesemiconductor material employed.

The interface formation of an embodiment can comprise the cleaning andtermination of material ‘1’.

The interface of an embodiment can comprise an oxide formed on material‘1’, including a native oxide as a part of material ‘2’. The thicknessof this oxide is an important determinant of device performance.Excessive oxide thicknesses (e.g., thickness exceeding 10-20 nm) canprovide an excessive contact resistance in series with thephotoconductive film, necessitating the application of an undesirablyincreased bias c/o the biasing circuit. In embodiments, the thickness ofthis native oxide is kept in the range of less than 5 nm.

The interface of an embodiment can comprise a further thin layer as partof material ‘2’, such as TiO2, generally included to modify the workfunction of the interface with the semiconductor to be placed on top.This layer can, in embodiments, provide selectivity in favour of onetype of charge carrier: for example, TiO2 can be configured such that,at the operating bias, it efficiently injects electrons into theconduction band of the photoconductive semiconducting layer; but, atthis same bias, it withdraws holes from the valence band of thephotoconductive semiconducting layer with much lower effectiveness. TiO2can be configured such that, at the operating bias, it efficientlyextracts electrons from the conduction band of the photoconductivesemiconducting layer; but, at this same bias, it injects holes into thevalence band of the photoconductive semiconducting layer with much lowereffectiveness.

The interface of an embodiment can comprise a further thin layer as partof material ‘2’, such as MEH-PPV, generally included to enable the flowof one type of charge carriers, such as holes, while blocking the flowof the other type, such as electrons.

The interface of an embodiment can comprise a thin layer as part ofmaterial ‘3’, possibly a self-organized molecular monolayer, designed toanchor on one side of the molecules to the underlying layers, and at theother terminus of the molecule to anchor to the semiconductor to beplaced atop, with the goal of ensuring controlled electroniccommunication, and also ensuring mechanical stability, e.g., goodadhesion between the materials making up the multilayer device.

The layered structure of an embodiment provides efficient charge carriertransfer through an interface. In embodiments, the layered structure canform a substantially ohmic contact with the photoconductivesemiconductor layer, providing for little or no depletion of thesemiconductor near the interface, and providing for efficient injectionand extraction of at least one type (e.g. electrons, holes) of chargecarrier. In embodiments, the layered structure can form a Schottkycontact with the photoconductive semiconductor layer, providing anenergetic barrier that must be overcome for charge carriers to beinjected and/or withdrawn. In embodiments, the layered structure canform a selective contact, providing considerably more efficientinjection of one type of charge carrier (e.g. electrons) than itprovides extraction of the other type (e.g. holes); and/or providingconsiderably more efficient withdrawal of one type of charge carrier(e.g. electrons) than it provides injection of the other type (e.g.holes).

The layered structure of an embodiment provides a work function of thecontact surface where the effective work function is determined by thematerial of the electrode, material of the interfacial layer, and itsthickness.

The layered structure of an embodiment provides blocking capability tosuppress the undesirable carrier transfer, for example as a layerproving electron trap states on the surface of metal electrode in caseof p-semiconductor photodetector device.

The layered structure of an embodiment provides strong bonding of thephotosensitive semiconductor material to the metal electrode.

The layered structure of an embodiment provides high temperaturestability of the metal electrode-semiconductor material interface.

The structure and composition of electronic devices of an embodimentwith an engineered interfacial layer includes but is not limited to ametal electrode comprising a conventional material used in semiconductormanufacturing being either readily oxidized, or nitridized, or both in achosen stoichiometric combination, such as as Ti, W, Ta, Hf, Al, Cu, Cr,Ag; or being resistive to oxidation or nitridization such as Au, Pt, Rh,Ir, Ru, graphite, amorphous carbon, graphene, or carbon nanotubes. Thesemetal electrodes can also be formed from alloys, conductive glasses, andvarious conductive intermetallics. The work function of the resultantelectrodes can be tuned through exposure to oxygen, nitrogen, or acombination thereof at a specific temperature for a specific time.

The structure and composition of electronic devices of an embodimentincludes an interfacial layer on the surface of the metal contact. Theinterfacial layer of an embodiment includes an oxide or intermetallic ofthe element of the electrode with the maximum thickness sufficient tokeep the ohmic characteristics of the contact but with the minimumthickness sufficient to create electron trap states. The structure canbe created or generated using PVD (physical vapor deposition), ALD(atomic layer deposition), CVD (chemical vapor deposition), ion cluster,ion beam deposition, ion implantation, anneal or other this filmdeposition method. Additionally, such films can be formed from aqueousand non-aqueous liquid formulations, which can include electrochemicaltechniques, to form hydroxides, oxides, fluorides, sulfides, sulfates,sulfites, sulphonates, phosphates, phosphonates, phosphides, nitrates,nitrites, nitrides, carbonates, carbides, and other types of salts orcomplexes of the said metals. The average thickness of the interfaciallayer can vary from a 0.1 nm-0.2 nm to 10 nm-50 nm depending onconductivity of the final interfacial layer, and work function of themetal electrode itself.

The interfacial layer of an embodiment includes another oxide depositedon the surface of the electrode, said oxide been doped TiO2, HfO2,Al2O3, SiO2, Ta2O5, Zn_(x)Al_(y)O, Zn_(x)Ga_(y)O, ZnIn_(x)Sn_(y)O, andsimilar p-conductive materials. Again, these materials can be depositedusing the methods mentioned earlier.

Additional properties of the interfacial layer are determined by thenecessity to form relatively strong chemical bond, preferably covalent,to the components of the semiconductor photosensitive layer. In casenone of the components of the photosensitive layer provide chemicalbonding to the interfacial layer the surface of the interfacial layer ismodified using organic by-functional molecules, where one type offunctional group provides selective bonding to the interfacial layersurface, while the second type of functional groups provides bonding toeither ligand or directly to semiconductor nanocrystals. These bondingmolecules can be formed on non-conductive alkane or aryl backbone or canbe formed on conductive backbone including aniline, acetylene, or othertypes of sp2 hybridized carbon. The functional groups to provide bondingto the oxidized surface of the electrode or surface of the interfaciallayer include but are not limited to silanes, siloxanes, silizanes,primary, secondary, or tertiary amines, imides, phosphates, oximes,carboxylates. The average length of the organic molecule forming theinterfacial layer can typically vary from 2 to 16 carbon atoms.

If the metal of the electrode is passive (e.g., Au, Pt, Cu, Ag, etc.)the interfacial layer can be formed from a molecule including twosimilar functional groups providing bonding directly to the metalsurface on one side and to a nanocrystal on another side. An examplewould be formation of Au—S—R—S—NC bond. Again, thickness andconductivity of the organic interfacial layer defined by the requiredelectronic device properties.

If the conductivity of the interfacial layer is exceeding the allowablelimits required be the electronic device parameters (for planarelectrode element) the continuous film can be patterned usingconventional patterning techniques.

In each electronic device with at least two electrodes one of theelectrodes can be made of a metal with one work function while anotherelectrode can made having a different workfunction and/or type ofconductivity (electron or hole).

For a vertical configuration of electronic device the same approach asabove is used for the bottom electrode while the interfacial layer ontop is formed by deposition of organic molecules or a thin transparentlayer of the semiconductor material.

Molecules described above are polymers with the degree of polymerizationfrom approximately 1 through approximately 10,000.

In forming a device described herein, generally, the device can beformed to include a consistent, reliable combination of material ‘1’ andmaterial ‘2’ which can be followed by the controlled formation ormaterial ‘3’ and the optically-absorbing layer ‘4’. For example, anembodiment can provide through material ‘1’ a highly conductive contacthaving resistivity less than 100 microohm*cm and a work function lyingbetween −2 eV and −4.5 V and lying between −2 eV and −4.2 eV. Anembodiment can provide through material ‘2’ a large-bandgap layer thatpermits the injection of electrons into the ensuing photosensitivesemiconductor layer, but blocks the extraction of holes from this layer.An embodiment can achieve a controlled thickness of a dopedsubstantially transparent oxide, such as n-type TiOx, as part of thefirst part of material ‘2’. For example, an embodiment can achieve aTiOx thickness in the range 2-20 which is controlled to within 1-5 nm;and where the TiOx has a specifically-chosen carrier density of 1×1018cm-3 with a tight band of control such as +/−10% in carrier density.

Manufacturing of a stack or configuration of layers of the devicedescribed herein can comprise: (1) formation of the metal, such as viathe sputtering of titanium in a nitrogen atmosphere, resulting in theformation of TiN; (2) subsequent processing that results in theformation of an interface layer such as a native oxide, such as TiOxNyor TiOx (it can be that this subsequent processing results in range ofpossible oxide thicknesses and dopings and carrier concentrations); (3)removal of the native oxide layer through an etch such as a sulfuricacid—hydrogen peroxide—deionized water etch, or an ammonium peroxideetch, or a physical etch such as argon sputtering, or a reactive sputteretch such as argon and hydrogen; in an embodiment this etch completelyremoves the oxide; a modest overetch to ensure complete removal can beimplemented; (4) an embodiment deposits a controlled thickness,controlled doping, and controlled-surface-terminated layer of an oxidesuch as TiOx, TiOxNy, or other interface layer. Methods such as physicalvapour deposition (including DC sputtering, RF sputtering, of a TiOxsource, a TiN source, or a Ti source, in the presence of O2, N2, or acombination thereof) can be employed to deposit these layers. Methodsalso include CVD and ALD where a precursor is first deposited on thesurface of the wafer, and a reaction proceeds at a controlledtemperature. In cases where TiOx is to be formed, precursors can beemployed.

Manufacturing of a stack or configuration of layers of the devicedescribed herein can comprise: (1) Formation of the metal, such as viathe sputtering of titanium in a nitrogen atmosphere, resulting in theformation of TiN; (2) In-situ transitioning to the deposition on top ofthis metal of an interface layer. These can include TiOx or TiOxNy. Thislayer can possess a controlled thickness, controlled doping, andcontrolled-surface-terminated layer of an oxide such as TiOx, TiOxNy, orother interface layer. Methods such as physical vapour deposition(including DC sputtering, RF sputtering, of a TiOx source, a TiN source,or a Ti source, in the presence of O2, N2, or a combination thereof) canbe employed to deposit these layers. Methods also include CVD and ALDwhere a precursor is first deposited on the surface of the wafer, and areaction proceeds at a controlled temperature. In cases where TiOx is tobe formed chemical precursors can be employed.

As described above, an encapsulating and/or passivating layer(s) can beused, above and/or below, the photoconductive layer, to preserveconsistent photoconductive features over time. The embodiments describedherein ensure a consistent gas environment (or lack of significantpresence of a gas) in the photoconductive layer. For example, vacuum,Argon, Nitrogen, Oxygen, Hydrogen, Carbon Dioxide, can be included orexcluded, in various proportions and to various degrees. Embodiments canexclude Oxygen, H2O, CO2, and include only either the absence of gasmolecules, or nonreactive materials such as Argon and/or Nitrogen. Topreserve consistent photoconductive features over time, an encapsulantlayer can be included whose purpose is to avoid gas exchange between thephotoconductive film and the region exterior to this film. Materialsemployed in an embodiment for this purpose include but are not limitedto: polyxylylene; As2S3 or As2Se3; Si3N4, SiO2, and mixtures thereof ieSiOxNy; oxides such as TiO2, HfO2, Al2O3, SiO2, Ta2O5, Zn_(x)Al_(y)O,Zn_(x)Ga_(y)O, ZnIn_(x)Sn_(y).

The encapsulant material can be preceded by a passivation layer,potentially in the form of a substantially single molecular monolayer.This first layer can serve to protect the encapsulated structure duringthe deposition of the encapsulant: for example, a layer of a materialsuch as polyxylylene can first be deposited, using a procedure that doesnot deleteriously alter the optoelectronic behaviour of thephotoconductive layer, and providing protection of the photoconductivelayer during ensuing encapsulation processes. It can, for example,protect the film from reactions resultant from oxygen and its radicalsthat are present during certain processes employed in the deposition ofoxygen-containing encapsulants such as SiOx, SiOxNy, etc.

In embodiments, typical thicknesses of the total encapsulant stack(which can comprise multiple layers) can range from a single monolayer(typically ˜nm or slightly sub-nm e.g. 5 A) to typically 1 micrometer.In embodiments, typical thicknesses of the total encapsulant stack canbe desired to be less less than 1-2 micrometers in order to perturbminimally the optical properties of the array.

In embodiments, included in at least one of the layers ‘1″2″3″4″5’ canbe materials that serve to getter molecules that could react withmaterials in the device, including materials which, if reacted, couldalter the photoelectrical properties of the device. Examples of reactivemolecules that could enter the device include O2 and H2O and O3.Examples of materials in the device that could have theirphotoelectrical properties altered by such reactions include material‘4’ NC, material ‘3’ adhesion, material ‘2’ interface, and ‘1’ metal.Examples of gettering moieties include borazons, borohydrides includingtetrahydroborates, catecholborane, L-selectride, lithium borohydride,lithium triethylborohydride, sodium borohydride, and uraniumborohydride. Examples of gettering moieties include hydrolysablesiloxanes.

The devices of an embodiment can include a strong chemical bond (e.g.,covalent), to the components of the semiconductor photosensitive layer.In case none of the components of the photosensitive layer providechemical bonding to the interfacial layer the surface of the interfaciallayer is modified using organic by-functional molecules, where one typeof functional group provides selective bonding to the interfacial layersurface, while the second type of functional group provides bonding toeither ligand or directly to semiconductor nanocrystals. These bondingmolecules can be formed on non-conductive alkane or aryl backbone or canbe formed on conductive backbone including aniline, acetylene, or othertypes of sp2 hybridized carbon. The functional groups to provide bondingto the oxide can include silanes, siloxanes, silizanes, primary,secondary, or tertiary amines, imides, phosphates, oximes, carboxylates.

Manufacturing processes of the devices of an embodiment can include awafer pre-clean using SC1 of 30 second duration and at 20° C. in a cleandry air ambient. Manufacturing processes of the devices of an embodimentcan include a rinse in de-ionized water of 30 second duration at 20° C.in a clean dry air ambient. Manufacturing processes of the devices of anembodiment can include drying the wafer involving a bake for aprescribed period of time (such as 30 seconds-24 hours) at a prescribedtemperature (such as 20, 70, 150, or 200 degrees C.) in a prescribedenvironment (such as clean dry air, vacuum, nitrogen, argon, or areducing atmosphere such as hydrogen, or a controlled oxidizingatmosphere containing an inert gas such as N2 or Ar and an oxidizing gassuch as O2).

Manufacturing processes of the devices of an embodiment can include thestipulation of maximum and minimum and average queue times in betweenother processes.

Manufacturing processes of the devices of an embodiment can includetreatments of substrates and quantum dot films including exposure toethanedithiol in acetonitrile at a prescribed temperature, such as 25degrees C., for a prescribed time, such as 20 seconds, in a prescribedatmosphere, such as N2. Manufacturing processes of the devices of anembodiment can include treatments of substrates and quantum dot filmsincluding exposure to hexanedithiol in acetonitrile at a prescribedtemperature, such as 25 degrees C., for a prescribed time, such as 20seconds, in a prescribed atmosphere, such as N2.

Manufacturing processes of the devices of an embodiment can include thedeposition of a dielectric capping layer, such as SiO2, at or beneath acertain temperature, such as 100° C., and to a specified thickness ofdielectric capping layer such as 100 degrees C.

Manufacturing processes of the devices of an embodiment can includelithographic definition of areas to be etched, followed by etching ofmaterials, including SiO2.

Manufacturing processes of the devices of an embodiment can include thedeposition of a dielectric capping layer, such as SiN, at or beneath acertain temperature, such as 100 degrees C., and to a specifiedthickness of dielectric capping layer such as 100 degrees C.

Manufacturing processes of the devices of an embodiment can includelithographic definition of areas to be etched, followed by etching ofmaterials, including SiN.

Manufacturing processes of the devices of an embodiment can includesilicon CMOS manufacturing including processing on 200 mm Si wafers anda standard Al/SiO₂ material technology at 0.11 micron nodes prior todeposition of the quantum dot layer. The CMOS manufacturing flow can becompleted with a patterned metal contact such as TiN.

Manufacturing processes of the devices of an embodiment can includeintegration of one Cu/TEOS/SiN HM single damascene layer on top of a vialayer followed by selective electroless deposition of Ni/Au stack.

Manufacturing processes of the devices of an embodiment can includesubstrate pre-treatment. Metal electrode and/or dielectric surfacemodification might be required to improve electrical contact or adhesionbetween the layers. Instead of wet preclean the wafer might be treatedby plasma or by a liquid-phase or vapor-phase process to form adhesionmono layers with controlled barrier height and density of surfacestates.

Manufacturing processes of the devices of an embodiment can include thedeposition of photosensitive films in which tight control over theambient atmosphere is provided to minimize and/or control the impact ofoxygen and moisture on film performance. They can include the use ofproduction tools equipped with O2 and H2O process monitors. Standardoperating procedures can be provided that ensure minimal, or controlledand consistent, exposure of materials (such as quantum dots and layersthereof) to air, including during chemical storage, and transfer offluids from storage containers to process tool tanks. Manufacturingprocesses can be compatible with chloroform and other solvents.

Manufacturing processes of the devices of an embodiment can includestabilizing the layer of quantum dots. These can include chemicalpost-treatment using diluted solutions of dithiols in acetonitrile.

Due to high sensitivity of QF to oxygen and moisture in ambient thequeue time between QF deposition and post-treatments should be minimizedand be done under N2 blanket. The same conditions apply to the queuetime between post-treatment B and dielectric cap deposition.

Manufacturing processes of the devices of an embodiment can include thesealing of the QF film from oxygen and moisture diffusion during thelifetime of the device. Low-temperature deposition of SiO₂/SiN stack canbe employed. Such processes should be performed at a substratetemperature below 100 degrees C. and at atmospheric pressure or at ashigh pressure as possible. Other process options can includelow-temperature spin-on glass processes or ultra-thin metallic filmswhich will not affect optical transmittance of the capping layers.

Process controls of the devices of an embodiment can include incomingwafer inspection prior to quantum dot film deposition. Inspection stepsof an embodiment include: a) inspection for defect density, such asusing bright field inspection; b) metal electrode work functioninspection, such as using Ultraviolet Photoelectron Spectroscopy (UPS)(the UPS method process control procedure can be performed on blanketprocess monitor wafers); c) leakage current and dielectric voltagebreakdown to be performed on TLM (test pixel array) structures. Thephotoelectric response of devices and film properties can be employed aspart of a process control.

In embodiments, material ‘4’ can include a material having a bandgap,and providing for the absorption of light within a range of wavelengthsof interest. In embodiments the photosensitive layer can includematerials such as Si, PbS, PbSe, CdS, CdSe, GaAs, InP, InAs, PbTe, CdTe,Ge, In2S3, Bi2S3, and combinations thereof. In embodiments thephotosensitive layer can include strongly light-absorbing materials suchas porphyrins. In embodiments, the photosensitive layer can includepassivating organic ligands such as ethanethiol, ethanedithiol,benzenethiol, benzenedithiol, dibenzenedithiol, pyridine, butylamine.

In embodiments, the photodetectors of an embodiment includephotosensitive devices that employ a light-sensitive energetic barriercontrolling the flow of at least one type of charge carrier.

In embodiments, the photodetectors can exhibit gain, wherein the ratioof the number of additional units of charge flowing each second to thenumber of photons impinging on a device each second can exceed unity,for example values lying in the approximately range 2-60.

In embodiments, the photodetectors can exhibit a high normalizedresponse, that is to say, a high ratio of photocurrent to dark currenteven at low light levels. For example, when 150 nW/cm2 of visible lightimpinge on the photodetectors, the ratio of photocurrent to lightcurrent can exceed 20. In general this value should be as high aspossible (while fulfilling other specifications, such as on lag and darkcurrent uniformity and photoresponse uniformity). Values as high as 100and greater are possible for the normalized response at 150 nW/cm2.

In embodiments, the photodetectors can exhibit a rapid temporalresponse, with the photo current (including following intenseillumination, such as 1 uW/cm2 on pixel and greater) settling to a valueclose to the dark current (such as one least-significant-bit from thedark current) within less than 1 second. Ideally the photocurrentsettles to this value within one exposure period, which can be 1/15 s,1/30 s, 1/200 s, 1/1000 s, or similar.

In embodiments, the current-voltage characteristic in the dark canexhibit, between zero and a first voltage, known as the saturationvoltage, a monotonically increasing functional relationship. This rangecan be referred to as the turn-on phase. The current-voltage canexhibit, between the first voltage and a second, larger, voltage, knownas the reach-through voltage, a monotonically increasing relationshiphaving a lower average slope than during the zero-to-first-voltagerange. This first-to-second-voltage range can be referred to as thesaturation range. At voltages greater than the second, or reach-through,voltage, the current-voltage relationship can exhibit an increase inslope relative to the first-voltage-to-second-voltage range. Thishighest-voltage range can be termed the post-reach-through range.

In embodiments, gain can be achieved when, under bias, the time for theflowing charge carrier (for example, electrons) to transit the device(i.e., the time to travel between two contacts, such as between leftside-material ‘1’ and right side-material ‘1’ in FIG. 2, or the time totravel between material ‘1’ and material ‘9’ in FIG. 3) exceeds theaverage lifetime of that charge carrier, when the contact that injectsthe flowing charge carrier (for example, electrons) also prevents theextraction of the other type of charge carrier, which can be termed theblocked carrier (for example, holes), and when the interface between thecontact that provides the flowing charge carrier (for example electrons)and the semiconductor film provides a low surface recombination velocityfor the blocked carrier (eg holes). This interface can be embodied inmaterial ‘2’ and material ‘3’ in FIG. 1, material ‘2’ and material ‘3’in FIG. 2 and also material ‘7’ and material ‘3’ in FIG. 2, and material‘2’, material ‘3’, material ‘5’ and material ‘8’ in FIG. 3.

More particularly, gain can be achieved when, under bias, the time forthe flowing charge carrier (for example, electrons) to transit thedevice exceeds the average lifetime of that charge carrier.Quantitatively, it can be said that the base transport factor, alpha_t,is less than but close to unity. This can be achieved if the minoritycarrier diffusion length for the flowing carrier carrier exceeds theseparation between the interface layers.

Furthermore, gain can be achieved when, under bias, the contact thatinjects the flowing charge carrier (for example, electrons) alsoprevents the extraction of the other type of charge carrier, which canbe termed the blocked carrier (for example, holes). Quantitatively, itcan be said that the emitter injection efficiency, gamma, is less thanbut close to unity. This can be achieved by using an interface layernear the flowing-carrier-injecting contact that blocks the extraction ofthe other type of charge carrier. This can be achieved by making theinterface layer from a large-bandgap material in which one band (such asthe conduction band) is substantially closely aligned in energy with thework function of the metal contact with which it is proximate; and whichis substantially misaligned in energy with the band in the semiconductorfrom which it is to block the extraction of charge carriers.

Moreover, gain can be achieved when, under bias, the interface betweenthe contact that provides the flowing charge carrier (for exampleelectrons) and the semiconductor film provides a low surfacerecombination velocity for the blocked carrier (eg holes).Quantitatively, it can be said that the recombination factor is lessthan, but close to, unity. This can be achieved if, within the minoritycarrier lifetime of the flowing carrier (eg electrons), only a smallfraction of the blocked-carrier (e.g. holes) recombine near theinterface between the contact that provides the flowing charge carrier(for example electrons) and the semiconductor film. This can requirethat the surface recombination velocity for the blocked carrier be lessthan 0.1 cm/s, for example 0.01 cm/s or less.

Referring to FIG. 2, embodiments can include methods and structurestaken to reduce the dark current passing between leftmost material ‘1’and rightmost material ‘1’. Embodiments can include the removal ofconductive moieties in the portion of material ‘3’ that reside betweenthe contacts leftmost material ‘1’ and rightmost material ‘1.’Embodiments can include the removal of conductive moieties such as metaloxides, metal hydroxides, organic contamination, polymer, conductiveoxides that reside between the contacts leftmost material ‘1’ andrightmost material ‘1’. Referring to FIG. 2, embodiments can include themodification of the interface between material ‘7’ and material ‘4’ inorder to control the recombination rate, the trapped charge, theadhesion, or a plurality of such properties at this interface.

Referring to FIG. 1, embodiments include controlling surface states suchas those present in interface layers ‘2’ and ‘3.’ Embodiments includestriking a metal such as TiN in material ‘1’ or a metal hydroxide suchas TiOx in material ‘2’ with xenon or other species or employing argonsputtering in order to control or modify the recombination rate on thesurface. Embodiments can include reducing the surface recombinationvelocity for charge carriers of one type to less than 0.1 cm/s or toless than 0.01 cm/2 at this interface.

Embodiments include the realization of small pixels with a pixel pitchof 0.9 um in each lateral dimension. Embodiments include the use ofnarrow vias such as 0.15 um. Embodiments include the use ofmetal-to-metal spacings of 0.14 um.

Embodiments described herein include an optically sensitive devicecomprising: a first contact and a second contact, each having a workfunction; an optically sensitive material between the first contact andthe second contact, the optically sensitive material comprising a p-typesemiconductor, and the optically sensitive material having a workfunction; circuitry configured to apply a bias voltage between the firstcontact and the second contact; the magnitude of the work function ofthe optically sensitive material being at least 0.4 eV greater than themagnitude of the work function of the first contact, and also at least0.4 eV greater than the magnitude of the work function of the secondcontact; the optically sensitive material having an electron lifetimethat is greater than the electron transit time from the first contact tothe second contact when the bias is applied between the first contactand the second contact; the first contact providing injection ofelectrons and blocking the extraction of holes; the interface betweenthe first contact and the optically sensitive material providing asurface recombination velocity less than 1 cm/s.

Embodiments described herein include an optically sensitive devicecomprising: a first contact; an n-type semiconductor; an opticallysensitive material comprising a p-type semiconductor; a second contact;the optically sensitive material and the second contact each having awork function shallower than 4.5 ev; circuitry configured to apply abias voltage between the first contact and the second contact; theoptically sensitive material having an electron lifetime that is greaterthan the electron transit time from the first contact to the secondcontact when the bias is applied between the first contact and thesecond contact; the first contact providing injection of electrons andblocking the extraction of holes; the interface between the firstcontact and the optically sensitive material providing a surfacerecombination velocity less than 1 cm/s.

Embodiments described herein include a photodetector comprising: a firstcontact and a second contact, each having a work function; an opticallysensitive material between the first contact and the second contact, theoptically sensitive material comprising a p-type semiconductor, and theoptically sensitive material having a work function; circuitryconfigured to apply a bias voltage between the first contact and thesecond contact; the magnitude of the work function of the opticallysensitive material being at least 0.4 eV greater than the magnitude ofthe work function of the first contact, and also at least 0.4 eV greaterthan the magnitude of the work function of the second contact; circuitryconfigured to apply a bias voltage between the first contact and thesecond contact; and the optically sensitive material configured toprovide a responsivity of at least 0.8 A/W when the bias is appliedbetween the first contact and the second contact.

The first contact of the photodetector of an embodiment is an injectingcontact and the second contact is a withdrawing contact.

The injecting contact of the photodetector of an embodiment isconfigured to inject a flowing carrier into the optically sensitivematerial with greater efficiency than the injecting contact withdraws atrapped carrier from the optically sensitive material.

The injecting contact of the photodetector of an embodiment isconfigured to withdraw a flowing carrier from the optically sensitivematerial with greater efficiency than the withdrawing carrier injects atrapped carrier into the optically sensitive material.

The optically sensitive material of the photodetector of an embodimentis a p-type semiconductor material.

The first contact of the photodetector of an embodiment comprises metaland wherein the second contact comprises metal.

The bias of the photodetector of an embodiment is in the range of about−0.1 Volts to −2.8 Volts and the flowing carrier is electrons.

The optically sensitive material of the photodetector of an embodimentcomprises nanoparticles selected from the group consisting of PbS, PbSe,PbTe, CdS, CdSe, CdTe, Si, Ge, or C.

Each nanoparticle of the photodetector of an embodiment includes anoxide on the surface of the nanoparticle.

An optically sensitive layer of the photodetector of an embodimentcomprises a material selected from the group consisting of PbSO4, PbO,PbSeO4, PbTeO4, SiOxNy, In2O3, sulfur, sulfates, sulfoxides, carbon andcarbonates.

The nanoparticles of the photodetector of an embodiment areinterconnected.

The injecting contact and the withdrawing contact of the photodetectorof an embodiment each comprise a material selected from the groupconsisting of Al, Ag, In, Mg, Ca, Li, Cu, Ni, NiS, TiN, or TaN.

The optically sensitive layer of the photodetector of an embodiment hasa dimension perpendicular to the direction of incident of light in therange of from 100 to 3000 nm.

A first carrier type of the photodetector of an embodiment is in themajority in the dark and a second carrier type is in the majority underillumination.

The first carrier type of the photodetector of an embodiment is holesand the second carrier type is electrons.

The first contact and the second contact of the photodetector of anembodiment comprise a shallow-work function metal.

The first contact and the second contact of the photodetector of anembodiment comprise each have a work function shallower than 4.5 ev.

The distance between the first contact and the second contact of thephotodetector of an embodiment is in the range of 200 nm to 2 um.

The flowing carrier of the photodetector of an embodiment has a mobilityof at least of at least 1E-5 cm2/Vs.

The p-type semiconductor material of the photodetector of an embodimentis a doped p-type material.

The bias of the photodetector of an embodiment is in the range of about+0.1 Volts to +2.8 Volts and the flowing carrier is holes.

The injecting contact and the withdrawing contact of the photodetectorof an embodiment each comprise a material selected from the groupconsisting of Au, Pt, Pd, Cu, Ni, NiS, TiN and TaN.

A first carrier type of the photodetector of an embodiment is in themajority in the dark and a second carrier type of the photodetector ofan embodiment is in the majority under illumination.

The first carrier type of the photodetector of an embodiment iselectrons and the second carrier type is holes.

The first contact and the second contact of the photodetector of anembodiment comprise a deep-work function metal.

The first contact and the second contact of the photodetector of anembodiment comprise each have a work function deeper than 4.5 ev.

The n-type semiconductor material of the photodetector of an embodimentis a doped n-type material.

The optically sensitive material of the photodetector of an embodimenthas a work function deeper than the work function of the first contactand the second contact by at least 0.3 ev.

The first contact and the second contact of the photodetector of anembodiment each comprise a material selected from the group consistingof Al, Ag, In, Mg, Ca, Li, Cu, Ni, NiS, TiN, TaN, n-type polysilicon andn-type amorphous silicon.

Embodiments described herein include a photodetector comprising: a firstcontact and a second contact; an optically sensitive material betweenthe first contact and the second contact, the optically sensitivematerial comprising an n-type semiconductor; the first contact and thesecond contact each having a work function deeper than 4.5 ev; circuitryconfigured to apply a bias voltage between the first contact and thesecond contact; and the optically sensitive material configured toprovide a photoconductive gain and a responsivity of at least 0.4 A/Wwhen the bias is applied between the first contact and the secondcontact.

The optically sensitive material of the photodetector of an embodimenthas a work function shallower than the work function of the firstcontact and the second contact by at least 0.3 ev.

The first contact and the second contact of the photodetector of anembodiment each comprise a material selected from the group consistingof Au, Pt, Pd, Cu, Ni, NiS, TiN, TaN, p-type polysilicon and p-typeamorphous silicon.

Embodiments described herein include a phototransistor comprising: afirst contact and a second contact; an optically sensitive materialbetween the first contact and the second contact, the opticallysensitive material comprising an n-type semiconductor; the first contactand the second contact each having a Schottky contact or work functiondeeper than 4.5 ev; circuitry configured to apply a bias voltage betweenthe first contact and the second contact; and the optically sensitivematerial having a hole lifetime that is greater than the hole transittime from the first contact to the second contact when the bias isapplied between the first contact and the second contact.

The flowing carrier of the photodetector of an embodiment is holes andthe trapped carrier is electrons.

Embodiments described herein include a phototransistor comprising: afirst contact and a second contact; an optically sensitive materialbetween the first contact and the second contact, the opticallysensitive material comprising a p-type semiconductor; the first contactand the second contact each having a Schottky contact or work functionshallower than 4.5 ev; circuitry configured to apply a bias voltagebetween the first contact and the second contact; and the opticallysensitive material having an electron lifetime when the bias is appliedbetween the first contact and the second contact; wherein the electronmobility of the optically sensitive material, the distance between thefirst contact and the second contact and the bias voltage are selectedsuch that the electron transit time from the first contact to the secondcontact is less than the electron lifetime when the bias is appliedbetween the first contact and the second contact.

The flowing carrier of the photodetector of an embodiment is electronsand the trapped carrier is holes.

Embodiments described herein include a phototransistor comprising: afirst contact and a second contact; an optically sensitive materialbetween the first contact and the second contact, the opticallysensitive material comprising an n-type semiconductor; the first contactand the second contact each having a Schottky contact or work functiondeeper than 4.5 ev; circuitry configured to apply a bias voltage betweenthe first contact and the second contact; the optically sensitivematerial having a hole lifetime when the bias is applied between thefirst contact and the second contact; wherein the hole mobility of theoptically sensitive material, the distance between the first contact andthe second contact and the bias voltage are selected such that the holetransit time from the first contact to the second contact is less thanthe hole lifetime when the bias is applied between the first contact andthe second contact.

The flowing carrier of the photodetector of an embodiment is holes andthe trapped carrier is electrons.

The photodetector of an embodiment comprises a p-type semiconductorcomprising p-doped silicon.

The photodetector of an embodiment comprises a p-type semiconductorcomprising GaAs.

The photodetector of an embodiment comprises a p-type semiconductorcomprising quantum dots/nano crystals.

The photodetector of an embodiment comprises a p-type semiconductorcomprising a network of interconnected nano crystals.

The photodetector of an embodiment comprises a p-type semiconductorcomprising nanocrystals and linker molecules.

The photodetector of an embodiment comprises a p-type semiconductorcomprising a compound semiconductor.

The photodetector of an embodiment comprises a p-type semiconductorcomprising PbS, PbS with PBSO₃.

Embodiments described herein include an optically sensitive devicecomprising: a first contact and a second contact, each having a workfunction; an optically sensitive material between the first contact andthe second contact, the optically sensitive material comprising a p-typesemiconductor, and the optically sensitive material having a workfunction; circuitry configured to apply a bias voltage between the firstcontact and the second contact; the magnitude of the work function ofthe optically sensitive material being at least 0.4 eV greater than themagnitude of the work function of the first contact, and also at least0.4 eV greater than the magnitude of the work function of the secondcontact; the optically sensitive material having an electron lifetimethat is greater than the electron transit time from the first contact tothe second contact when the bias is applied between the first contactand the second contact; the first contact providing injection ofelectrons and blocking the extraction of holes; and the interfacebetween the first contact and the optically sensitive material providinga surface recombination velocity less than 1 cm/s.

The work function of the first contact and the second contact of thedevice of an embodiment are each shallower than 4.5 ev.

The bias of the device of an embodiment is in the range of about −0.1Volts to −2.8 Volts.

The optically sensitive material of the device of an embodimentcomprises a plurality of nanoparticles, wherein each of thenanoparticles has an oxide on a surface of the respective nanoparticle.

The optically sensitive material of the device of an embodimentcomprises nanoparticles selected from the group consisting of PbS, PbSe,PbTe, CdS, CdSe, CdTe, Si, Ge, or C.

The optically sensitive layer of the device of an embodiment comprises amaterial selected from the group consisting of PbSO4, PbO, PbSeO4,PbTeO4, SiOxNy, In2O3, sulfur, sulfates, sulfoxides, carbon andcarbonates.

The optically sensitive material of the device of an embodimentcomprises a plurality of interconnected nanoparticles.

The first contact and the second contact of the device of an embodimenteach comprise a material selected from the group consisting of Al, Ag,In, Mg, Ca, Li, Cu, Ni, NiS, TiN, or TaN, TiO2, TixNy, ITO, Ru, TiSi,WSi2, TiOx doped with B, TiOx doped with C, TiOx doped with Co, TiOxdoped with Fe, TiOx doped with Nd, TiOx doped with N.

The first contact and the second contact of the device of an embodimentare separated by a distance in the range of 200 nm to 2 um and theelectron mobility in the optically sensitive material is at least 1E-5cm2/Vs.

The optically sensitive material of the device of an embodiment isconfigured to provide a responsivity of at least 0.8 A/W when the biasis applied between the first contact and the second contact.

Embodiments described herein include an optically sensitive devicecomprising: a first contact; an n-type semiconductor; an opticallysensitive material comprising a p-type semiconductor; a second contact;the magnitude of the work function of the optically sensitive materialbeing at least 0.4 eV greater than the magnitude of the work function ofthe second contact; the optically sensitive material having an electronlifetime that is greater than the electron transit time from the firstcontact to the second contact when the bias is applied between the firstcontact and the second contact; the n-type semiconductor providinginjection of electrons and blocking the extraction of holes; and theinterface between the n-type semiconductor and the optically sensitivematerial providing a surface recombination velocity less than 1 cm/s.

The n-type semiconductor of the device of an embodiment comprises amaterial selected from the group consisting of TiO2, TiO2 that has beenchemically reduced, TiO2 that has been oxidized, CdTe, CdS, CdSe, Si, ornanoparticles selected from the group consisting of PbS, PbSe, PbTe,CdS, CdSe, CdTe, Si, Ge, or C.

The bias of the device of an embodiment is in the range of about −0.1Volts to −2.8 Volts.

The optically sensitive material of the device of an embodimentcomprises a plurality of nanoparticles, wherein each of thenanoparticles has an oxide on a surface of the respective nanoparticle.

The optically sensitive material of the device of an embodimentcomprises nanoparticles selected from the group consisting of PbS, PbSe,PbTe, CdS, CdSe, CdTe, Si, Ge, or C.

The optically sensitive material of the device of an embodimentcomprises a plurality of interconnected nanoparticles.

The first contact and the second contact of the device of an embodimentare separated by a distance in the range of 200 nm to 2 um.

The first contact and the second contact of the device of an embodimenteach comprise a material selected from the group consisting of Al, Ag,In, Mg, Ca, Li, Cu, Ni, NiS, TiN, TaN, TiO2, TixNy, ITO, Ru, TiSi, WSi2,TiOx doped with B, TiOx doped with C, TiOx doped with Co, TiOx dopedwith Fe, TiOx doped with Nd, TiOx doped with N.

Embodiments described herein include a photodetector comprising: a firstcontact and a second contact, each having a work function; an opticallysensitive material between the first contact and the second contact, theoptically sensitive material comprising a p-type semiconductor, and theoptically sensitive material having a work function; circuitryconfigured to apply a bias voltage between the first contact and thesecond contact; the magnitude of the work function of the opticallysensitive material being at least 0.4 eV greater than the magnitude ofthe work function of the first contact, and also at least 0.4 eV greaterthan the magnitude of the work function of the second contact; circuitryconfigured to apply a bias voltage between the first contact and thesecond contact; and the optically sensitive material configured toprovide a responsivity of at least 0.8 A/W when the bias is appliedbetween the first contact and the second contact.

The work function of the first contact and the second contact of thephotodetector of an embodiment are each shallower than 4.5 eV.

The bias of the photodetector of an embodiment is in the range of about−0.1 Volts to −2.8 Volts.

The optically sensitive material of the photodetector of an embodimentcomprises nanoparticles selected from the group consisting of PbS, PbSe,PbTe, CdS, CdSe, CdTe, Si, Ge, or C.

The optically sensitive layer of the photodetector of an embodimentcomprises a material selected from the group consisting of PbSO4, PbO,PbSeO4, PbTeO4, SiOxNy, In2O3, sulfur, sulfates, sulfoxides, carbon andcarbonates.

The first contact and the second contact of the photodetector of anembodiment each comprise a material selected from the group consistingof Al, Ag, In, Mg, Ca, Li, Cu, Ni, NiS, TiN, TaN, TiO2, TixNy, ITO, Ru,TiSi, WSi2, TiOx doped with B, TiOx doped with C, TiOx doped with Co,TiOx doped with Fe, TiOx doped with Nd, TiOx doped with N.

The first contact and the second contact of the photodetector of anembodiment are separated by a distance in the range of 200 nm to 2 umand the electron mobility in the optically sensitive material is atleast 1E-5 cm2/Vs.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in a sense of “including,but not limited to.” Words using the singular or plural number alsoinclude the plural or singular number respectively. Additionally, thewords “herein,” “hereunder,” “above,” “below,” and words of similarimport, when used in this application, refer to this application as awhole and not to any particular portions of this application. When theword “or” is used in reference to a list of two or more items, that wordcovers all of the following interpretations of the word: any of theitems in the list, all of the items in the list and any combination ofthe items in the list.

The above description of embodiments is not intended to be exhaustive orto limit the systems and methods to the precise forms disclosed. Whilespecific embodiments of, and examples for, the embodiments are describedherein for illustrative purposes, various equivalent modifications arepossible within the scope of the systems and methods, as those skilledin the relevant art will recognize. The teachings of the embodimentsprovided herein can be applied to other systems and methods, not onlyfor the systems and methods described above.

The elements and acts of the various embodiments described above can becombined to provide further embodiments. These and other changes can bemade to the embodiments in light of the above detailed description.

What is claimed is:
 1. An optically sensitive device comprising: a firstcontact; an n-type semiconductor; an optically sensitive materialcomprising a p-type semiconductor; and a second contact; a magnitude ofthe work function of the optically sensitive material being at least 0.4eV greater than a magnitude of the work function of the second contact;the optically sensitive material having an electron lifetime that isgreater than an electron transit time from the first contact to thesecond contact when bias is applied between the first contact and thesecond contact; the n-type semiconductor providing injection ofelectrons and blocking extraction of holes; and the interface betweenthe n-type semiconductor and the optically sensitive material providinga surface recombination velocity less than 1 cm/s; the n-typesemiconductor being an oxide of the first contact formed throughexposure to water, oxygen, or other oxidizing species, as a result ofthe presence of exposed metal in the first contact and where, underelectrical bias, the first contact preventing the extraction of holes.